Along with the advancement in technology, the applications of organic conductivity, semiconductor materials and polymeric materials have been developing in an extremely fast pace. Currently, more and more photoelectric industries have directed toward the use of organic materials as the basis of research and development. This is because a variety of organic materials are available at inexpensive prices, and compared to the fragility of the conventional glass and semiconductors, the organic materials are flexible to meet different design requirements. Meanwhile, in recent years, computers having extremely high operating speed and practical usefulness have been associated with increasingly grown networks and become closely related to people's daily life and work, which in turn brings the development in display devices. The manufacturing of an organic field effect transistor with high performance has, therefore, become an important key factor in providing high quality display devices.
A transistor can be generally divided into four parts, namely, a gate, an insulating layer, a source and a drain located at two opposite sides, and a semiconductor layer. The gate, the source, and the drain represent three different electrodes. Metals often used for forming these three electrodes are gold, silver, and alloy. The amplitude of the voltage supplied to the gate determines the on/off condition of the transistor; and the voltage of the drain determines the current flowed between the drain and the source while the transistor is in the on state. Due to the above-described electric field operation at the gate, we call this type of transistor as a field effect transistor. The efficiency of a transistor is determined by the carrier mobility, the current on/off ratio and the aspect ratio of the transistor structure. The higher the carrier mobility is, the more signals that can be processed. Generally speaking, a transistor having a semiconductor layer made of an organic material usually has carrier mobility lower than that of a transistor having a semiconductor layer made of an inorganic material. As to the effect of the aspect ratio of the transistor structure, it is not discussed herein.
Generally, the property of the insulating layer has relatively large influence on the property of the organic transistor. The surface condition of the insulating layer is an important factor in determining the carrier mobility of the organic semiconductor. For example, in the case of a polymeric material, poly(3-hexylthiophene) (P3HT), a good self-assembly crystal feature can occur on a relatively smooth surface of the insulating layer. However, this problem is not concerned in terms of a common organic transistor manufactured on a silicon substrate because a smooth and dense thermally oxidized layer can be grown on a substrate to obtain relatively high carrier mobility and low leak current at the gate. But, it is usually impossible to obtain such good device properties when the polymeric material semiconductor is further applied to the cheap and highly variable glass or plastic substrate. This is because the insulating layer formed on the glass or plastic substrate is pretty rough and has many defects. In this case, the leak current at the gate passing through the insulating layer will largely increase and the carrier mobility is relatively poor.
Therefore, it is desirable to develop a method for manufacturing an organic field effect transistor with high carrier mobility and high on/off ratio on a glass substrate or a plastic substrate at low manufacturing cost.
In view of the above-mentioned problems in the prior art, on the basis of engaging in research for many years and a lot of practical experience, the inventor proposes an organic field effect transistor and a manufacturing method thereof in an attempt to overcome the existing problems.